As is well known, metal-containing waste forms a serious environmental problem. This is particularly true of waste in which the presence of heavy metals which can be leached relatively rapidly, such as cadmium, lead and zinc, entails a potential environmental hazard. Moreover, the metal-containing waste materials form a very heterogeneous group of materials which comprises, inter alia, metal-containing muds, sludges, filter cakes, metal and filter dusts, batteries, accumulators, printing plates, composites, laminates, catalysts and pickling fluids from, e.g., the electroplating industry. Such waste materials show very large differences among themselves with respect to physical appearance and composition (type and content of the metals and minor components present). Depending on the type of waste and the source, in the Netherlands alone this involves many tonnes up to tens of thousands of tonnes per metal-containing waste product per year.
Out of the abovementioned enormous amount of metal-containing waste materials, only 5%, according to estimates, are being worked up in metal recovery processes. This processed portion of the metal-containing waste materials primarily involves waste materials having a (very) high content of valuable metals and a low content of minor components, such as scrap iron, scrap zinc, scrap lead and cabling waste (recovery of copper). By far the greater part of the metal-containing waste materials is therefore dumped, either on the operator's own plant site or at a dump suitable for this purpose.
In principle, two routes are available for processing complex metal-containing waste materials, namely: [1] the hydrometallurgical route and [2] the pyrometallurgical route. Both techniques are used for producing metals from primary raw materials (ores). With respect to processing most metal-containing waste materials, however, these conventional hydro- and pyrometallurgical processes do not always provide the direct answer, since:
the waste materials, in terms of complexity regarding physical properties and chemical composition, differ from natural ores; PA1 waste materials may contain combinations of metals which do not occur in natural ores; PA1 waste materials may contain components which have an adverse effect on the hydro- and pyrometallurgical processes, and PA1 virtually all metals including iron are brought into solution, which latter product needs to be removed in the subsequent process, which requires a large amount of chemicals and often affords an iron product which should be regarded as a hazardous waste.
Given the major need for an effective reprocessing method for metal-containing waste, Applicant has therefore carried out in-depth research regarding a uniformly applicable method for extracting (at least part of) the metals from the multitude of metal-containing waste materials.